Consider inferences between mapped type templates lower priority

[weswigham]

Similarly to how inferences between mapped type constraints are lower priority. In general, inferences through a mapped type are usually just worse than other inferences, if available, due to the (potentially lossy) mapping operation the mapped type is doing.

Fixes #44092

[weswigham]

@typescript-bot user test this
@typescript-bot test this
@typescript-bot run dt

[typescript-bot]

Heya @weswigham, I've started to run the extended test suite on this PR at 99110e9. You can monitor the build here.

[typescript-bot]

Heya @weswigham, I've started to run the parallelized Definitely Typed test suite on this PR at 99110e9. You can monitor the build here.

[typescript-bot]

Heya @weswigham, I've started to run the parallelized community code test suite on this PR at 99110e9. You can monitor the build here.

[typescript-bot]

The user suite test run you requested has finished and failed. I've opened a PR with the baseline diff from master.

[sandersn]

The lower priority makes sense to me, but it seems like a risky change to make in the RC because it will likely result in another complex followup bug. I vote to hold this for 4.4 unless you know that the problem is widespread.

[DanielRosenwasser]

@typescript-bot pack this

[typescript-bot]

Heya @DanielRosenwasser, I've started to run the tarball bundle task on this PR at 99110e9. You can monitor the build here.

[typescript-bot]

Hey @DanielRosenwasser, I've packed this into an installable tgz. You can install it for testing by referencing it in your package.json like so:

{
    "devDependencies": {
        "typescript": "https://typescript.visualstudio.com/cf7ac146-d525-443c-b23c-0d58337efebc/_apis/build/builds/103289/artifacts?artifactName=tgz&fileId=A55A16C587F60DF7E2A4B95F02939F25AB0C274D50F5790CB101D9A07CCF6AD902&fileName=/typescript-4.4.0-insiders.20210518.tgz"
    }
}

and then running npm install.

---

There is also a playground for this build and an npm module you can use via "typescript": "npm:@typescript-deploys/[email protected]".;

[DanielRosenwasser]

@typescript-bot cherry-pick this to release-4.3

[typescript-bot]

Heya @DanielRosenwasser, I've started to run the task to cherry-pick this into release-4.3 on this PR at 99110e9. You can monitor the build here.

[typescript-bot]

Hey @DanielRosenwasser, I've opened #44189 for you.

[sandersn]

@weswigham @DanielRosenwasser Is this ready to go into master and 4.3 respectively?

[weswigham]

I mean, we should probably ship it in the nightly for a bit, right?